Ink jet markers have been known in the art for some time. A typical marker has at least one output nozzle having an orifice; and, when a marking cycle is initiated, ink under pressure is directed to the output nozzle or ink already routed to the output nozzle is ejected through the orifice under pressure when an ink retaining valve in the nozzle is opened.
Several problems attend such devices, particularly if ink is to be applied to targets that are in relative motion with respect to the marker. Timing the beginning of ink ejection in devices having ink release valves produces, at best, inaccurately positioned marks. Position control in devices applying pressure to initiate ink ejection is usually even less accurate, often by several orders of magnitude. Additionally, when ink is ejected from such devices, the texture of the jet of previously unatomized ink is often initially inconsistent, resulting in a similarly inconsistent target mark.
After a mark has been produced, and ink ejection is to be terminated, removing pressure from the ink does not provide a substantially instantaneous cessation of ink flow. Closing a valve to terminate ink ejection provides a more instantaneous cessation of ink flow but has an attending problem of ink sometimes being left in the output nozzle and possibly jamming the valve partially open or jamming the nozzle orifice closed, these results frequently having serious, disruptive consequences, such as delayed or intermittent ink ejection or no ink ejection at all, during subsequent marking cycles.
U.S. Pat. No. 4,661,822 to Hirota et al. discloses an ink jet printer that includes a method for attempting to overcome the problem of having a print nozzle clogged by ink residue. The Hirota ink jet printer includes a pump to supply ink under pressure to the print nozzle. When the pressure of the ink supplied to the nozzle exceeds a certain value, or when the deflection of the ejected ink is improper, either of these conditions being indicative of a clogged nozzle, the pump is intermittently driven so that the ink pressure at the nozzle is oscillated in an attempt to remove the nozzle blockage.
The Hirota method for removing nozzle blockage represents a substantial improvement in the operating efficiency of ink jet printers; however, its effectiveness remains limited by the adhesion, composition and viscosity of the ink fouling the nozzle, especially when compared with the effectiveness of the pneumatic means disclosed by the present application for dissipating any ink remaining in a nozzle after ink ejection has been terminated and with the mechanical means disclosed by the present application for removing nozzle blockage during a period of ink ejection.